1. Technical Field
The technical field generally relates to the field of wireless communications. More particularly, the technical field relates to a system and method for efficient transmission of a supplemental channel request message (SCRM) for a reverse supplemental channel (R-SCH) in a wireless communications device.
2. Description of the Related Art
Recent advances in wireless communications and the rapid expansion of use of the Internet have greatly increased the demand for mobile computing. Technologies for allowing a large number of system users to share a communication system, such as Code Division Multiple Access (CDMA) technology, have played a critical role in meeting that demand.
CDMA is a digital radio-frequency (RF) technique defined in the Telecommunications Industry Association/Electronics Industries Association Interim Standard-95, entitled xe2x80x9cMOBILE STATION-BASE STATION COMPATIBILITY STANDARD FOR DUAL-MODE WIDEBAND SPREAD SPECTRUM CELLULAR SYSTEM,xe2x80x9d which was published in July 1993 and which is incorporated herein by reference.
CDMA communication devices are assigned a unique code, and each device uses its code to spread its communication signals across a common spread-spectrum bandwidth. As long as the communication device has the correct code, it can successfully detect and select its signal from among other signals concurrently transmitted over the same bandwidth.
Other multiple access techniques include time division multiple access (TDMA) and frequency division multiple access (FDMA) systems. There are also analog frequency modulation (FM) based wireless communication systems, such as the Advanced Mobile Phone System (AMPS). In addition, many wireless communication devices combine communications capabilities with global position system (GPS) techniques. Some wireless communication systems are capable of operating using multiple techniques, such as CDMA and GPS, or on different frequency bands, such as cellular or Personal Communication Services (PCS) bands.
The increased reliability of mobile communications has led to a demand for remote wireless computing where a computing device, such as a laptop computer or palmtop computer, is remotely coupled to a computer network (e.g., the Internet) via the mobile telephone.
FIG. 1 is a functional block diagram illustrating a wireless data connection. In FIG. 1 a terminal equipment (TE) 10 may be a laptop, palmtop, or other conventional computing device. The TE 10 is coupled to a wireless communication device, such as a mobile telephone (MT) 12, usually through a mobile system modem (MSM) 14. The MSM 14 may be incorporated into the TE 10 or into the MT 12.
The TE 10, MT 12 and MSM 14 may conveniently be collectively characterized as a mobile station (MS) 16, as indicated by the dashed lines in FIG. 1. In fact, the MS 16 may be an integrated device comprising a TE 10, an MT 12, and an MSM 14.
The wireless communication system of FIG. 1 also includes a base station transceiver system (BTS) 18. The BTS 18 communicates with the MS 16 via a wireless communication link 20.
To establish a communication link between the MS 16 and the BTS 18, communication signals are exchanged. Various protocols and standards provide a framework for implementing a wireless data connection. The actual implementation of hardware and software within that framework is left to the discretion of the designer.
Such implementations may take advantage of the fact that in most communication sessions the MS 16 receives much more data from the BTS 18 (forward channel communication) than the MS 16 transmits to the BTS 18 (reverse channel communication). Thus, less bandwidth may normally be assigned for reverse channel communication, with additional bandwidth assigned as the amount of data to be transmitted increases. In one such implementation the BTS 18 is configured to assign a reverse supplemental channel (R-SCH) with an assigned data rate and burst length to an MS 16 in response to a supplemental channel request message (SCRM) from the MS 16.
Typically, at call setup the MS 16 and the BTS 18 will negotiate a maximum agreed R-SCH data rate. The negotiated rate may be based on various factors, such as the maximum rate the MS 16 can support and the amount of available power resources of the MS 16 to be allocated to reverse channel communication. The MS 16 sends a non-zero length SCRM to the BTS 18 to indicate a R-SCH is needed in response to certain triggering events.
For example, the MS 16 may send an SCRM when it does not have an R-SCH assignment and a certain number of bytes are buffered for transmission to the BTS 18. The MS 16 may also send an SCRM when the assigned R-SCH data rate is too high or too low for the current operating conditions. The MS 16 may also send a zero-length SCRM to cancel a R-SCH.
The MS 16 may request a R-SCH. In response, the BTS 18 may assign a R-SCH and notify the MS 16 of the assignment with an extended supplemental channel assignment message (ESCAM) or a universal handoff direction message (UHDM). Moreover, the BTS 18 may not grant the requested data rate or may not grant the request at all. In addition, there may be a delay in granting the request. The BTS 18 may also send a retry delay message to the MS 16.
One of the problems that has been encountered is xe2x80x9cfloodingxe2x80x9d of the BTS 18 with SCRMs, even though a triggering event may have occurred. Thus, an MS 16 may transmit too many SCRMs, including SCRMs which are not likely to result in a more optimal assignment of R-SCHs by the BTS 18. In addition, when the amount of data to be transmitted exceeds the capacity of a currently assigned R-SCH, there can be a significant delay between the termination of the current R-SCH burst and the start of a subsequent R-SCH.
Therefore, it can be appreciated that there is a significant need for an efficient system and method for controlling transmission of an SCRM for a R-SCH in a wireless communication device.
The system and method described herein are directed to controlling transmission of supplemental channel request messages (SCRM) by a wireless communication device. In one embodiment, the system may be configured to prevent transmission of a SCRM in response to a predetermined triggering event until a fixed period of time has elapsed since the last transmission of a SCRM in response to the predetermined triggering event. In another embodiment, the system may be configured to prohibit transmission of a SCRM when a reverse supplemental channel (R-SCH) burst has been assigned but has not started.